Lewis Acids And Bases
The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair, completing its stable form, which requires two electrons.
The modern-day definition of Lewis acid, as given by IUPAC is a molecular entity (and the corresponding chemical species) that is an electron-pair acceptor and therefore able to react with a Lewis base to form a Lewis adduct, by sharing the electron pair furnished by the Lewis base. This definition is both more general and more specific—the electron pair need not be a lone pair (it could be the pair of electrons in a π bond, for example), but the reaction should give an adduct (and not just be a displacement reaction).
A Lewis base, then, is any species that donates a pair of electrons to a Lewis acid to form a Lewis adduct. For example, OH− and NH3 are Lewis bases, because they can donate a lone pair of electrons.
Some compounds, such as H2O, are both Lewis acids and Lewis bases, because they can either accept a pair of electrons and donate a pair of electrons, depending upon the reaction.
Usually the terms Lewis acid and Lewis base are defined within the context of a specific chemical reaction. For example, in the reaction of Me3B and NH3 to give Me3BNH3, Me3B acts as a Lewis acid, and NH3 acts as a Lewis base. Me3BNH3 is the Lewis adduct.
Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR3 where R can be an organic substituent or a halide. For the purposes of discussion, even complex compounds such as Et3Al2Cl3 and AlCl3 are treated as trigonal planar Lewis acids. Metal ions such as Na+, Mg2+, and Ce3+, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base. Other reactions might simply be referred to as "acid-catalyzed" reactions.
Read more about Lewis Acids And Bases: Depicting Adducts, History, Lewis Acids, Lewis Bases, Hard and Soft Classification
Famous quotes containing the words lewis, acids and/or bases:
“It’s an ideal house for delirium tremens.”
—Dodie Smith, and Lewis Allen. Rick Fitzgerald (Ray Milland)
“The new American finds his challenge and his love in the traffic-choked streets, skies nested in smog, choking with the acids of industry, the screech of rubber and houses leashed in against one another while the townlets wither a time and die.”
—John Steinbeck (1902–1968)
“In the beginning was the word, the word
That from the solid bases of the light
Abstracted all the letters of the void....”
—Dylan Thomas (1914–1953)